Retractable tap changer operating mechanism



United States Patent 3,206,999 RETRACTABLE TAP CHANGER OPERATING MECHANISM Earl F. Roth, Pittsburgh, Pa., assignor to Allis-Chalmers Manufacturing Company, Milwaukee, Wis. Filed Mar. 21, 1962, Ser. No. 181,419 2 Claims. (Cl. 74-511) This invention relates to tap changer mechanisms and in particular to a means for manually selecting a variety of voltages from a tapped transformer.

In certain types of power transformers, the secondary winding is provided with a plurality of taps. By connecting movable contacts to different pairs of these taps, the output voltage of the transformer is varied inasmuch as the ratio of the secondary winding to the primary winding is varied. Since the voltage output of a power transformer may be rather high, it is necessary that the equipment used to connect various pairs of taps is of a heavy type. Generally, such equipment will include a pair of heavy duty contacts which are movable to different stationary contacts connected to the taps of the winding by an operating shaft. In the event the transformer is of a three phase type, three sets of tap changing mechanisms will be used, all of which may be simultaneously operated by one operating shaft.

In the prior art, this operating shaft may be of a manual type which extends through an aperture in the transformer housing. In such an arrangement it is desirable that the bushing supporting the operating shaft at its point of passage through the housing is of a sealing type in order to prevent contamination of the tank. An external handle may be mounted on the shaft in order to manually rotate the shaft and its associated movable contacts.

.My invention provides for a means in which the operat ing shaft is normally wholly contained in the housing and yet may be rotated with conventional hand tools. This arrangement further eliminates any special sealing device since the operating shaft does not normally extend through the housing. Briefly my invention comprises an operating shaft which is in coaxial alignment with a hole in the housing. The shaft has a portion which has resiliency limited to a line along its axis. Under normal operations the shaft is maintained within the housing in a compressed state by a removable plug which is positioned in the housing aperture. The length of the shaft is further dimensioned so that the shaft extends through the aperture and past the periphery of the housing upon removal of the plug. In this manner, a conventional wrench is all that is needed to effect a tap change.

Thus, it is one object of this invention to provide a new and improved switch apparatus.

Another object of this invention is to provide a new and improved tap changing mechanism which is normal y enclosed and which may be operated without the need of specially designed tools.

Another object of this invention is to provide a new and improved manually operated tap changing mechanism for a tapped transformer having a retractible operating shaft.

These and other objects will be apparent to those skilled in the art to which this invention relates from the following description when read in connection with the accompanying drawing in which:

FIG. 1 is a view in partial section of a three phase tapped power transformer containing the tap changer mechanism of this invention;

FIGr. 2 is an enlarged top view in elevation of the opering shaft of this invention in its extended position;

*FIG. 3 is a view in elevation in partial section along line III-III of FIG. 2; and

FIG. 4 is a view similar to FIG. 3 with the operating shaft in its retracted position and rotated clockwise 90.

Referring to FIG. 1, a housing 11 is shown containing a conventional type three phase power transformer 12 with tapped windings 14. The housing comprises a tank 16 and a cover 17. An upper end frame 19 clamps laminated steel core 20 of the transformer and also may be the supporting structure for a tap changer unit 22. Associated with the windings of the three phase transformer are three mechanisms 23, each having six contacts 25 vertically positioned above the upper end frame. Three sets of movable cont-acts 26 are used to change taps and are controlled by a rotatable operating shaft 28. The rotary action of the operating shaft is transmitted through a bevel gear arrangement 29 which in turn rotates a second shaft 31 on which movable contacts 26 are mounted. Thus, all three phases of the transformer are tap changed together, eliminating any chance of one phase being connected differently from another.

FIGS. 2 and 3 illustrate the operating shaft 28 in its extended and operating position for making a tap change. Tank cover 17 has an aperture 33 through which the operating shaft extends. The operating shaft includes a rod 34 which is coupled to bevel gears 29. Rod 34 is telescoped within a hollow cylindrical sleeve 36 in a sliding fashion. The sleeve has a pair of longitudinal guide tracks 37 which cooperate with a roll pin 39 in the rod. The upper end of the sleeve is closed by a shaft head device 41 coupled to the sleeve by a roll pin 42. Shaft head 41 may have a square top 43 which may be easily turned with a conventional wrench. Within sleeve 36 is a spiral compression spring 44 which is seated between end 46 of the rod and end 47 of shaft head 41. In the position illustrated in FIG. 3, spring 44 is under a minimum amount of compression. Extending from the base of the rod at a right angle is a stop pin 50. A second stop pin 51 extends from housing 53 which encloses the gears 29. Pins 50 and 51 limit the extent of counterclockwise rotation of operating shaft 28.

In the particular embodiment illustrated in FIG. 2, the transformer has five different taps identified with the letters A through E appearing on an index plate 55 supported by a plate holder 56. The plate is also supported by a cover extension comprising a short section of threaded pipe coupling 58 which extends about aperture 33 in the cover. The pipe coupling further defines the aperture 33 and also serves as a receptacle for a plug 60 (FIG. 4) threadedly engaged in the coupling. The plug has a head 61 for engagement with a wrench or other hand tool.

In normal operation, operating shaft 28 is in the retracted position of FIG. 4 where it is held by pipe plug 60. Thus spring 44 is under maximum compression and the operating shaft is in effect at a minimum length as a result of hollow sleeve 36 which is telescoped an additional amount over operating shaft rod 34. With the three tap changing mechanisms 23 at position A, we may assume that it is desired to move the mechanisms to position E. The operator may put a wrench on the head 61 of the plug 60 and withdraw it from the pipe coupling 58. As the plug is backed off, the operating shaft 28 slowly extends outwardly. This is achieved by spring 44 which is constantly exerting an upward force on end 47 of shaft head 41. As the spring expands, shaft head 41 moves upwardly and therefore causes sleeve 36 to also move upwardly and slide along roll pin 39 engaging guide tracks 37. Upon complete removal of plug 60, shaft 28 is in the position shown in FIG. 3. A wrench may be applied to shaft head top 43 to rotate the tap changing mechanism to position E. An indicating pin 63 extending from shaft head 41 will indicate when the tap changing mechanism is at position E. Stop pin 64 extending from the gear box housing 53 prevents further clockwise rotation of the shaft 28.

Thus, by providing the operating shaft with a resilient portion utilizing a compression spring, the shaft may be varied in its length. Guide tracks 37 which engage roll pin 39 in the rod further effect transmission of a rotary action to the mechanism. It is to be noted that pipe coupling 58 is primarily provided to adequately engage pipe plug 60 in a sealing relationship. In the event that the transformer cover on the tank is of sufficient thickness it is apparent that this coupling may be omitted with index plate 55 then being mounted directly on the cover.

It will be apparent to those skilled in the art that other changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

What is claimed is:

1. In combination: a housing having a hole and an exterior plug receptacle surrounding said hole, an apparatus within said housing, an operating.v shaft rotatably coupled to said apparatus and in coaxial alignment with said hole, said shaft having a first portion with a variable length, said first portion including a hollow cylindrical sleeve with a longitudinal guide track, one end of said sleeve being closed and extending through said hole past the periphery of said housing and plug receptacle when said shaft is at its maximum length, said shaft having a second portion partially telescoped within said sleeve and having a pin in sliding engagement with said guide track, a biased spiral spring disposed within said sleeve in abutment with said closed end and said second portion, said shaft being adapted at its free end to receive means for turning said shaft, and a removable plug threadedly engaged in said receptacle for urging said first shaft portion toward said second shaft portion whereby said shaft is at a reduced length and fully contained within said housing.

2. In combination,

a housing containing apparatus and having a hole and ceptacle for maintaining said, shaft portion in a biased state whereby said shaft is at a reduced length and fully contained within said housing.

References Cited by the Examiner UNITED STATES PATENTS 9/73 Moflfett 251-292 X 4/ 89 Powell.

7/17 Ewart 74-548 X 11/ 17 Remington 251-293 X 4/24 Beerworth 74-504 2/25 Tyrrell 251-291 X 7/ 25 Swanson 74-503 2/51 Cerniak 74-545 X 9/51 Grommes 74-548 1/52 Magers 251-293 X 5/60 Wezner 74-548 X FOREIGN PATENTS 1/ 41 Germany.

3 5 7 Germany.

2/ 26 Great Britain.

BROUGHTON G. DURHAM, Primary Examiner.

DON A. WAITE, Examiner. 4 p 5" 

1. IN COMBINATION: A HOUSING HAVING A HOLE AND AN EXTERIOR PLUG RECEPTACLE SURROUNDING SAID HOLES, AN APPARATUS WITHIN SAID HOUSING, AN OPERATING SHAFT ROTATABLY COUPLED TO SAID APPARATUS AND IN COAXIAL ALIGNMENT WITH SAID HOLE, SAID SHAFT HAVING A FIRST PORTION WITH A VARIABLE LENGTH, SAID FIRST PORTION INCLUDING A HOLLOW CYLINDRICAL SLEEVE WITH A LONGITUDINAL GUIDE TRACK, ONE END OF SAID SLEEVE BEING CLOSED AND EXTENDING THROUGH SAID HOLE PAST THE PERIPHERY OF SAID HOUSING AND PLUG RECEPTACLE WHEN SAID SHAFT IS AT ITS MAXIMUM LENGTH, SAID SHAFT HAVING A SECOND PORTION PARTIALLY TELESCOPED WITHIN SAID SLEEVE AND HAVING 